Derivative Instruments and Risk Management Activities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Increase Decrease In Floor Plan Interest Expense Due To Interest Rate Hedges	$ 2,800	$ 2,500	$ 5,500	$ 4,900
Derivatives in cash flow hedging relationship
Interest rate swap contracts	1,804	(3,844)	(4,709)	(6,364)
Location of Loss Reclassified from OCI into Statements of Operations
Floor Plan Interest Expense	$ (10,015)	$ (10,329)	(19,362)	(21,242)
Floorplan Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Floor Plan Interest Expense			(5,470)	(4,884)
Other Interest Expense [Member]
Location of Loss Reclassified from OCI into Statements of Operations
Interest Expense			(845)	(722)
Interest Rate Swap Contracts [Member]
Derivatives in cash flow hedging relationship
Interest rate swap contracts			$ (4,709)	$ (6,364)